1. Field of the Invention
The invention relates to an alkaline fuel cell electrode catalyst and an alkaline fuel cell that employs the electrode catalyst as well as manufacture methods for the alkaline fuel cell electrode catalyst and the alkaline fuel cell.
2. Description of the Related Art
Japanese Patent No. 3360485 discloses a fuel cell that uses a reformed gas from methane or methanol as a fuel. In the fuel cell of Japanese Patent No. 3360485, the anode electrode (fuel electrode) has a function of producing pure hydrogen from methane or methanol supplied as a fuel. Concretely, this anode electrode is constructed of three layers, that is, a catalyst inner layer in contact with an electrolyte membrane, a porous base material disposed on an outer side of the catalyst inner layer, and a catalyst outer layer disposed on the outer side of the porous base material. A platinum catalyst is used in the catalyst inner layer and the catalyst outer layer.
According to Japanese Patent No. 3360485, when the anode electrode of a fuel cell is supplied with a fuel such as methane or the like, hydrogen in the fuel is extracted and separated into protons and electrons mainly due to the action of catalyst particles in the catalyst outer layer, and the electrons are received again on other catalyst particles so as to form a hydrogen gas. The carbon monoxide (CO) produced at this time is adsorbed and retained to catalyst particles in the catalyst outer layer. The hydrogen gas produced in the catalyst outer layer of the anode electrode passes through the porous base material to reach the catalyst inner layer. The hydrogen gas is separated again into electrons and protons by the action of the catalyst particles in the catalyst inner layer, and the protons pass through the electrolyte membrane to reach the cathode electrode (oxygen electrode).
That is, according to Japanese Patent No. 3360485, pure hydrogen is produced in the catalyst outer layer of the anode electrode, and CO or the like also produced at the same time directly becomes adsorbed in the catalyst outer layer. Therefore, only pure hydrogen moves into the porous base material so that the interior of the porous base material is filled with pure hydrogen. As a result, only the pure hydrogen diffuses in the catalyst inner layer. Thus, even in the case where a fuel containing carbon, such as methane, methanol, etc., is used, the adverse effects of CO on the catalyst inner layer are restrained and the functions of the anode electrode are secured.
In order to improve the power generation performance of fuel cells, development of an electrode catalyst that has high catalytic activity is desired. Besides, particularly in the case where a fuel other than pure hydrogen, such as alcohol or the like, is used, it is important to efficiently extract hydrogen by decomposing the fuel and therefore improve the utilization rate of the fuel.
In this respect, Japanese Patent No. 3360485 provides a technology, for the case where methane or methanol is used as a fuel, which produces pure hydrogen from methane or the like and supplies the pure hydrogen to the catalyst inner layer so as to restrain the adverse effects of CO on the anode electrode of the catalyst inner layer. However, Japanese Patent No. 3360485 does not concern achieving high efficiency in the extraction of hydrogen from methane or methanol as a fuel. In the case where, as in Japanese Patent No. 3360485, hydrogen gas is produced from methane or the like in the catalyst outer layer, and is supplied to the catalyst inner layer, and protons are produced from the hydrogen gas in the catalyst inner layer, two stages of catalytic reaction in the catalyst outer layer and the catalyst inner layer are undergone. Therefore, it is considered that the catalytic reaction rate of the anode electrode will decline and the power generation performance of the fuel cell will be lowered.
Incidentally, the fuel cell disclosed in Japanese Patent No. 3360485 employs a proton exchange membrane as an electrolyte membrane, so that the power generation reaction is conducted in an acidic environment. In contrast, the alkaline fuel cell employs an electrolyte membrane that allows permeation of anions therethrough, so that the power generation reaction is conducted in an alkaline environment. Therefore, in the alkaline fuel cell, a metal that tends to degrade in an acidic environment may be used as an electrode catalyst. Hence, since the metal used as an electrode catalyst may be selected from a wide variety of choices, an electrode catalyst that has high catalytic activity while achieving a cost reduction of the electrode catalyst by using a metal other than platinum (Pt) is expected to be developed. Besides, heightened catalytic activity of the electrode will make it possible to achieve high output of the fuel cell even if a fuel other than pure hydrogen is supplied directly to the electrode catalyst. Thus, an electrode catalyst may efficiently extract hydrogen by decomposing the supplied fuel and thus improve the fuel utilization rate so as to further improve the power generation performance of the alkaline fuel cell while expanding the range of choices of the fuel of the fuel cell is desired to be developed.